Pump protection system

ABSTRACT

To protect the pump of a whirlpool bath against running dry and against blockage at the inlet, a pressure (or flow) sensor 14 senses pump pressure and generates a signal to keep a switch S2 in the pump motor electrical supply circuit closed. If the pressure signal ceases owing to blockage or running dry, the switch S2 opens. A manual override button 15 is held ON to close switches S1a and S1b in the power circuit for start-up. The sensor 14 and manual button 15 are preferably air pressure devices. Switch S1a is preferably an air-signal-operated latching switch whereby with the pump operating, the button 15 can be operated to switch the pump off. Relays RLA 1 and 2 may be used in conjunction with the electrical switches. A bleed hole may be provided between the button 15 and switch S1b to limit the period of time for which the motor could be run, with the bath empty, by prolonged inadvertent actuation of the button 15.

This invention relates to a pump protection system for a liquid pump,notably a water pump, and particularly although not exclusively for apump of a whirlpool bath. The invention also relates to a pumpinstallation having a protection system.

In whirlpool baths, a pump is provided to pump the water from the bath(for example through a pump inlet located at the drain outlet of thebath) and to circulate the water back to the bath through nozzles in theside of the bath, thereby to create turbulence.

It is known to provide a protection system for a whirlpool pump whichdetects the presence of water in the system to protect the pump againstrunning dry. One such system employs two electrodes let into thepipework which sense the presence of water by the establishment ofelectrical continuity between the electrodes. Another system senses astatic pressure head of water in the pipework.

An obvious disadvantage of the electrode system is that of usingelectrical connections or elements in or near to the water, with theinherent difficulties of ensuring absolute safety. With the staticpressure sensor, a disadvantage is that waves or vigorous water movementin a bath can result in inadvertent actuation or de-actuation.

However, the main disadvantage is that whilst known systems can protecta whirlpool pump against running dry, they are not adapted to protect awhirlpool pump from overheating in event of the inlet to the pumpbecoming blocked, as can happen in a whirlpool bath when an object suchas a bathing cap, face flannel or the like covers the circulation pumpinlet.

An aim of the present invention is to provide an improved protectionsystem for a pump so as to protect it against damage and which isapplicable to whirlpool pumps and possibly in other applications ofpumps also.

According to one aspect of the present invention, there is provided aprotection system for a liquid pump, comprising a sensor for sensing aflow characteristic of liquid flow through the pump and for producing asignal indicative of the existence of that characteristic, means forrendering the pump operative or inoperative in dependence upon thepresence or absence of a signal from the sensor, and a manually operableoverride means operable to render the pump operative in the absence of asignal from the sensor.

Preferably, the means for rendering the pump operative or inoperative,and/or the manual override means, acts on the power supply to a motorfor driving the pump, conveniently an electrical supply to an electricmotor.

Alternatively, it would be possible for the signal from the sensor to beused to put the pump into a non-pumping mode, e.g. by adjusting theswashplate to a zero angle if a pump of that type is used, bydis-engaging a clutch in the pump drive, or by opening a by-pass duct sothat the pump merely pumps a limited amount of water around its ownby-pass circuit; this last alternative would be useful for protection ifthe pump inlet from the bath became blocked rather than for protectionagainst running dry for which the pump drive would have to be renderedinoperative.

Advantageously, the manually operable override means is operable also asa switch to switch off the pump.

The sensor which senses the flow characteristic may be located at anysuitable location so as to determine the flow condition through thepump, either in the pump itself, at its immediate inlet or outlet, or atany position between the pump circuit inlet from the bath and thedischarge nozzles into the bath.

The sensor is preferably adapted to sense, as the flow characteristic,the dynamic operating pressure generated by the pump. This may be sensedat the inlet or outlet of the pump though the latter is simpler sincethe sensor merely has to sense a positive dynamic presure or an absenceof such pressure. A pressure sensor at the inlet would have to becapable of sensing the normal reduced dynamic pressure (the operatingsuction pressure), an absence of pressure (if the pump runs dry) and areduction below normal suction pressure as would occur if the pump inletbecame blocked.

As an alternative to sensing the dynamic operating pressure, it might bepossible to use a flow motion sensor in which case it could be locatedat the inlet or outlet since it would produce a signal by flow movementrather than in response to pressure as such.

The use of a dynamic operating pressure sensor is preferred howeverbecause it facilitates the use of non-electrical signals. Thus,according to a preferred feature of the invention, the sensor forsensing a dynamic pressure is adapted to generate a pneumatic signalwhich is used to operate a pneumatic-pressure responsive switchcontrolling the pump. Likewise, the manual override means preferablycomprises a manual pneumatic switch which generates a pneumatic signalfor operating a pressure-responsive switch. In this way the sensing andmanual override switch means are non-electrical and are completely safe.This is especially relevant in the case where the pump is driven by anelectric motor.

Air signal-generating devices are conveniently used as the pneumaticsensor and manual override means, preferably of the type in which adiaphragm or bellows is acted upon by the water pressure, or is pressedby a person using the manual switch, thereby to generate in each case anair pressure signal which is used to actuate an air-pressure diaphragmactuated switch. However, other forms of pressure transducers could beused to generate the dynamic pressure or override signals.

In the case where the pump is driven by an electric motor, the signalresponsive switches may act directly upon the electrical power supply tothe motor which drives the pump, provided the power current does notexceed the rating of the switches; for higher HP motors it is necessaryto use relays so that the air-pressure actuated electrical switchescontrol the operation of relays which in turn switch the power supplycurrent.

Equally, if another form of power supply were used, the switches couldeither act directly upon that power supply or indirectly via servomeans.

Where the manual override serves also as an `OFF` switch to switch thepump off, it is conveniently connected to two signal-responsiveswitches, one for overriding the protection system and the other alatching switch establishing a control line in series with theprotection switch connected to the sensor. Thus with the pump operating,actuation of the manual override will serve to switch off the latchingswitch and render the pump inoperative.

In use, the pump protection system of the invention is effective both toprotect a pump against running dry, as for example if the water from awhirlpool bath is drained out while the pump is operating, and alsoautomatically to switch the pump off if the inlet becomes blockedcausing a change in the flow conditions through the pump.

To avoid damage if the manual override switch is held on with no waterin the pump, means is preferably provided to limit the period of time ofeffective operation of the manual override switch, such as a small bleedhole or calibrated orifice in the pneumatic line connecting that switchto the pressure-responsive switch.

The pump protection system of the invention is particularly suitable fora whirlpool bath but could be also useful to protect the circulationpump of a swimming pool or the pressure developing pump of a shower.

In domestic applications and where electric motors are used, safety isof paramount importance and the use of pneumatic switches and sensors isseen as an advantageous feature. According to a second aspect of theinvention, therefore, there is provided a domestic pump installation fora bath or shower, having a pump driven by an electric motor, a pumpprotection system including a sensor for sensing operating conditionsand a manually operable switch for controlling the pump, wherein thesensor and manually operable switch are pneumatic signal-generatingdevices connected to actuate remote electrical switching controlling themotor.

For safety reasons also, the pump is preferably made of a non-conductingmaterial, e.g. plastics, and all the water contacting parts are isolatedfrom the pump motor.

The invention may be put into practice in a number of ways but certainspecific embodiments will now be described by way of example only withreference to the accompanying drawings, in which:

FIG. 1 is a pump protection system in accordance with the invention, fora whirlpool, bath using direct electrical switching;

FIG. 2 is a system similar to that of FIG. 1 but using indirectelectrical switching via relays;

FIG. 3 is an embodiment of a diaphragm pressure sensor;

FIG. 4 is an embodiment of an air-pressure actuable switch, being apressure ON, no pressure OFF switch; and

FIG. 5 is an embodiment of an air-pressure actuable switch, being alatching switch.

The pump protection system shown in FIG. 1, for a domestic whirlpoolbath, is for protecting a pump driven by an electric motor (not shown)which is connected to the usual line and neutral power supply lines 10and 11 and to an earth 12.

Supply to the motor is controlled directly by two switches S2 and S1a inthe line 11 which are air-pressure actuable switches, for example of theconstruction shown in FIGS. 4 and 5 to be referred to later. Switch S2is a simple ON-OFF switch being ON when the actuating air-pressuresignal is present (positive) and OFF when there is no such signal.Switch S1a in contrast is a latching switch which first sets to ON whenan air-pressure signal is received by the switch and then remains ONwhen the signal is no longer there, the switch only changing to OFF whena further positive air-pressure signal is received.

Connected in parallel with switch S2 is a further air-pressure actuableswitch S1b which is like switch S2. Switches S1b and S2 are not ofexactly the same type, though they are similar: S2 is a pressure switchdesigned, due to the choice of spring internally, to switch at a rangeof pressures which is adjustable using a fine adjustment screw; S1b issimply a switch with no adjustability.

The air-pressure signals for actuating the switches S2, S1a and S1b aregenerated by two devices, namely a diaphragm pressure sensor 14 and adiaphragm push-button 15. Instead of diaphragm devices, bellows devicescould be used.

The sensor 14 is, when installed, located in the outlet pipe leadingfrom the pump so that in operation it senses the dynamic pressure ofwater created by the pump at its outlet. Thus, the increased pressure inthe water during pumping operation causes the diaphragm or bellows todeflect and generate an air pressure signal which is fed via an airsignal line 17 to the switch S2 to actuate that switch to close it (ON).

The push-button 15 is a manually operable device. When the button ispressed it deflects a diaphragm or bellows to send air signals via twoair signal lines 18 and 19 to the switches S1a and S1b. From thepush-button 15 there is a single air line, labelled 18/19, which dividesat a tee-piece 16 in the "control box" to the individual lines 18 and19, as close to the switches S1a and S1b as possible to minimise thevolume of air between those switches and the push-button 15.

Switches S1a and S1b do not need to be adjustable. The push-button 15 ispressed until sufficient air pressure is developed to trip thoseswitches. When the button 15 is released those air-pressure signalscease.

The operation is as follows: Before the whirlpool bath is filled, i.e.with the pump dry and not operating, no air signal is generated by thesensor 14 so switch S2 remains open (OFF) and no power gets to themotor. (A safeguard is provided to prevent damage if the motor is triedto be run in this condition by someone pressing the push-button 15, aswill be referred to later). When there is water in the bath, the userpresses push-button 15 to generate air signals to close both switchesS1a and S1b thereby to connect power to the motor and start the pumpwhich almost immediately generates an outlet water pressure. Thisdynamic water pressure operates the sensor 14 to send an air signal toswitch S2 to close that switch.

When the push-button 15 is released its signals cease and switch S1bopens but latching switch S1a remains closed. Power thus continues tothe motor through both switches S1a and S2.

If whilst the pump is running the inlet to the pump becomes blocked, thepump outlet pressure drops, the sensor 14 no longer generates an airpressure signal and therefore switch S2 will open to protect the pumpfrom overheating. The same protection procedure would be followed if thebath drained whilst the pump is operating.

The pump can now only be restarted (once the blockage has been removedor the bath re-filled) by pressing the push-button 15 twice, once tore-set the latching switch to OFF and again to close both switches S1aand S1b to energise the pump motor.

The advantage of using a latching switch that has to be manually re-setby the push-button 15 is that with the pump operating normally, when theuser wants to switch if off, e.g. to empty the bath, he simply pressesthe push-button 15 which causes the latching switch S1a to open.

The sensor 14 is designed to operate at a pressure of around 1 or 2p.s.i. This may be adjustable, either at the sensor 14 and/or at theswitch S2. The operating air pressure of the push-button device 15and/or of the switches S1a and S1b may but need not normally beadjustable.

The sensor 14 and push-button device 15 are both non-electrical and areconnected to the electrical switches S1a, S1b and S2 only by the airsignal lines 17,18,19 so that their operation is quite safe even thoughthey are operated in wet conditions. The electrical supply lines 10 to12 and the motor itself may be located at a remote, safe distance fromthe bath interior.

As an optional feature, there may be provided a safeguard to prevent theON switch push-button 15 from being held ON whilst the whirlpool bath isempty, which might unwittingly cause the pump motor and pump to runwhilst dry for a prolonged period as long as the button 15 is held down;this might happen if a small child played with the bath when empty or anobject was inadvertently placed over or against the button 15. To avoidthis, a carefully sized bleed hole (not shown) may be provided in theline 18/19 or line 19 which has the effect of limiting the time forwhich the switch S1b will remain closed. The time is limited accordingto the diameter of the bleed hole and might typically be 3 seconds for ableed hole diameter of 0.3 mm.

In practice, the bleed hole may conveniently be drilled in the tee-piece16; or it may be a calibrated orifice built in to the tee-piece or atsome other location. The bleed hole must be of sufficiently smalldiameter to avoid too much loss of air from the system whilst switchingis actually taking place.

Naturally there could be other ways of providing such a safeguard thoughother arrangements would involve detecting the presence of water eitherin the pump or in the suction pipe by either electrical or mechanicalmeans, and since one of the purposes of the pump protection system inaccordance with the invention is to avoid using such devices the bleedhole arrangement or some other time limiting safeguard feature ispreferred. However, such other arrangements could be used in combinationwith the pump protection system of the invention, if required.

The protection system shown in FIG. 2 works in principle in a similarway to that shown in FIG. 1 and where appropriate the same referenceshave been used.

The main difference is that the switches S1a, S1b and S2 instead ofacting directly in the power supply line 10 are connected between line10 and neutral 11 so that by including suitable current limiters (notshown) they do not carry the full supply current. Rather, the switchescontrol relays RLA 1 and RLA 2, the switch contacts of which areconnected in the line 10.

In this embodiment, separate air lines 18 and 19 are shown connected tothe push-button 15 though in practice there would probably again be asingle line dividing at a tee-piece as for the embodiment of FIG. 1.

In operation, when the whirlpool bath (and therefore the pump pipework)have water in them and the push-button 15 is pressed, the latchingswitch S1a closes thereby causing energisation of relay RLA 1 andclosing of its switch contacts in line 10; also switch S1b closesthereby causing energisation of relay RLA 2 and closing of its switchcontacts in line 10; the pump motor is thus energised and the pumpgenerates water pressure which actuates the sensor 14 which in turncloses switch S2.

The push-button 15 is then released and switch S1b will open but relayRLA 2 will remain energised through switch S2 as long as the pump outletpressure is maintained. Also, relay RLA 1 will remain energised throughthe latching switch S1a.

If the pump inlet gets blocked or the water drains out of the pump, thepump outlet pressure will fall, sensor 14 will no longer generate asignal, switch S2 will therefore open to de-energise RLA 2 and itsswitch contacts will open to cut out the pump motor.

To re-start the pump when normal operating conditions are restored, thepush-button 15 must be pressed twice; the first time will un-latchswitch S1a and the second pressing closes both switches S1a and S1b asbefore.

To stop the pump whilst it is running normally, e.g. before emptying thebath, the push-button 15 is simply pressed once to unlatch switch S1aand open relay switch contacts RLA 1.

A safeguard to prevent prolonged operation of the motor with the bathempty by holding down the button 15, may be provided by means of a bleedhole in the line 19 as decribed above for FIG. 1.

The diaphragm pressure sensor 14 shown in FIG. 3 is located in a branch20 of the pump outlet duct 21 leading from the pump to a nozzle ornozzles in the whirlpool bath wall. A small plastics collar 22 iscemented in the end of the branch 20 to hold the sensor 14 in place.Water pressure in the duct 21 and branch 20 acts to deflect thediaphragm 25 and cause a small air pressure signal to pass along thesignal line 17.

The air-pressure responsive switch shown in FIG. 4 has a receivingchamber 27 to which an air pressure signal is fed by the signal line 17or 19, a wall of the chamber 27 being a diaphragm 28 which deflectsupwardly to pivot a rocker 30 which depresses the button 31 of amicroswitch 32. When the button 31 is depressed, the contacts 33 of themicroswitch are closed. A return spring 35 ensures that the diaphragm 28relaxes and that the button 31 can move to its OFF position when the airsignal in line 17 or 19 is no longer present. An adjusting screw 37 canbe used to set the air pressure at which the air signal actuates theswitch.

The air-pressure responsive latching switch shown in FIG. 5 is generallysimilar to the ON-OFF switch shown in FIG. 4, the difference being thatdeflection of the diaphragm 28 causes movement of a latch even when thediaphragm 28 relaxes. When the diaphragm 28 deflects a second time itraises both the latch member 40 and the latch release member 41 tounlatch member 40 and allow it to fall when the diaphragm again relaxes,causing the microswitch to be switched off.

In the above embodiments, the pressure diaphragm 14 is intended to beused in the pump outlet. If a pressure sensor is to be used in the pumpinlet it would need to respond only at a pre-determined suction pressurebut not if the pressure falls below that value or rises to zero.Possibly two pressure transducers would be needed to achieve this.

Also, whilst the above description has referred to positive actuatingsignals, it will be appreciated that embodiments could be designed witha converse arrangement where for example the switches are operated whena signal ceases.

The pump protection system could also be used with pump assisted showerunits. Such pumps are necessary when the header tank is located at toolow a level to give a sufficient head for showering. They are usuallyinstalled on the down-stream side of the shower valve. However, if thepump system pumps, simultaneously, hot and cold feds to the shower mixervalve, the protection of the pump system might have to be based on thealternative system which senses a change in pressure on the suctionline, since otherwise a system sensing pressure at the pump outlet mightnot switch off the pump if only one of the supplies became blocked anddamage to that side of the dual impeller pump could ensue.

I claim:
 1. A protection system for a liquid pump, comprising aprotection switch connected to a sensor for sensing a flowcharacteristic of liquid flow through the pump and for producing asignal indicative of the existence of that characteristic, means forrendering the pump operative or inoperative in dependence upon thepresence or absence of a signal from the sensor, a manual override meansfor rendering the pump operative in the absence of a signal from thesensor and an override switch to switch off said pump, said overrideswitch being connected to two signal-responsive switches, one foroverriding the protection system and the other a latching switchestablishing a control line in series with said protection switch. 2.The protection system as claimed in claim 1, in which the means forrendering the pump operative or inoperative, and/or the manual overridemeans, acts on the power supply to a motor for driving the pump.
 3. Theprotection system as claimed in claim 1, in which the pump is driven byan electric motor, and in which the signal responsive switches actdirectly upon the electrical power supply to the motor which drives thepump.
 4. The protection system as claimed in claim 1 in which the pumpis driven by an electric motor, and in which the signal responsiveswitches are connected to operate relays (which switch) to control theelectrical power supply to the motor.
 5. The protection system asclaimed in claim 1 includes a domestic pump installation for a bath orshower, having a pump driven by an electric motor wherein the sensor andmanually operable switch are pneumatic signal generating devicesconnected to actuate remote electrical switching controlling the motor.6. The protection system as claimed in claim 1, in which the sensorincludes means to sense a positive dynamic pressure and an absence ofsuch pressure generated at the pump outlet.
 7. The protection system asclaimed in claim 6, in which the means to sense said dynamic pressure isadapted to generate a pneumatic signal which is used to operate apneumatic-pressure responsive switch controlling the pump.
 8. Aprotection system as claimed in claim 6 or 7, in which the manualoverride means is a manual pneumatic switch which generates a pneumaticsignal for operating a pressure-responsive switch.
 9. A protectionsystem as claimed in claim 6, in which the pneumatic sensor and/ormanual override means are air signal-generating devices.
 10. Aprotection system as claimed in claim 8, in which the airsignal-generating devices each include a movable diaphragm or bellows.11. The protection system as claimed in claim 1, in which means isprovided to limit a period of time of effective operation of the manualoverride means.
 12. The protection system as claimed in claim 11, inwhich the manual override means is a manual pneumatic switch connectedby a pneumatic line to a pressure-responsive switch, and in which themeans for limiting the period of time of effective operation of theoverride means comprises a bleed hole in the pneumatic line.
 13. Theprotection system as claimed in claim 1, wherein said sensor is a flowmotion sensor positioned at said pump inlet means for rendering the pumpoperative or inoperative in dependence upon the presence or absence of asignal from the sensor.
 14. The protection system, as claimed in claim13, wherein the sensor is a flow motion sensor positioned at the pumpoutlet.
 15. The protection system as claimed in claim 1, wherein saidsignal received from the sensor activates means for rendering the pumpoperative or inoperative in dependence upon the presence or absence ofsaid signal.